How much flood risk does Madison County actually carry?
Madison County lands at the 92.3th percentile of FEMA's National Risk Index for flooding, "Relatively Moderate" territory — a middling flood hazard by national standards — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 1.4 times a year. County-wide, not parcel-specific: FEMA's real flood-zone map is queried live, never shipped as a download.
Mandatory flood insurance compliance in Madison County
Madison County is one of the counties where FEMA's own denominator for mandated flood-zone structures is missing, so no compliance rate is shown rather than a guessed one — the data quality guide covers how common this is. Across all residential structures in Madison County, not just the ones FEMA mandates, 0.8% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
How Madison County compares nationally
Madison County sits at rank 259 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 281 of 3144 by population (1 is biggest). Madison County, Illinois is home to about 263,017 people across 715.522 square miles of land.
Your street may differ from Madison County's average
Across all of Madison County's 105,162 residential structures, 824 carry an NFIP policy today — a county-wide count that still can't tell you one address's own mapped zone.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Madison County's numbers. See the data quality guide for why Madison County, like hundreds of other counties, doesn't get a clean compliance percentage.